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That car doesn't have the welds in the trunk reinforced. Once those welds separate, the mounts flex and tear badly. If the plates are welded underneath but the trunk welding is still damaged, the entire floor just keeps getting hammered. We have been highly suggesting everyone that has the reinforcement done at our shop to have the trunk reinforcement done in addition to the four mounts underneath the car. We have seen a few cars that were even worse than this. One was not salvageable because the welding labor would have been cost prohibitive. one of the worst cars that we repaired had the entire diff dragging on the ground with all four mounts completely torn out of the body.

I guess ill have to get the trunk done with you guys now to... Scary thoughts of this happening... But first i just need to fix my input shaft seal leaking for the time being... Kind of strapped for cash

I went through this years ago. Brace it right so it never happens again

Something like this is the only fairly certain fix. Even with the "reinforcements" in the end it's just one little block held together at the two points of sheet metal, only afterward it's spaced over a little more area, but that increase is barely anything at the top.

None of the subframe reinforcement kits on the market today reinforce the floor itself. This is a known problem with BMW E46 models and as the cars get up there in mileage and in power we will see continual problems. We are going to do a special reinforcement on the drag car to keep the rear end from literally tearing off.

We have also fixed some E46's that have come to us with that type of damage. It takes a lot more reinforcement.

That car doesn't have the welds in the trunk reinforced. Once those welds separate, the mounts flex and tear badly. If the plates are welded underneath but the trunk welding is still damaged, the entire floor just keeps getting hammered. We have been highly suggesting everyone that has the reinforcement done at our shop to have the trunk reinforcement done in addition to the four mounts underneath the car. We have seen a few cars that were even worse than this. One was not salvageable because the welding labor would have been cost prohibitive. one of the worst cars that we repaired had the entire diff dragging on the ground with all four mounts completely torn out of the body.

The installation of my HPF subframe plates cost me almost 2k in labor because I told my welder to go way beyond the standard installation instructions. He went over all that trunk stitching and a lot more other areas too. I have to dig the photos out. They are buried somewhere.

I told him to go "crazy" for the overkill. I winced at the bill, but now the sting is well taken out of all the money I paid. . I didnt know. How could I? I just had this strong suspicion that the standard installation just would not be good enough for MY purposes. Now, I see it is not good enough for some other's as well. Oh, boy! My condolences to BattaM3

I am now wondering if I still need to do even MORE. I am showing the pics in this thread to my welder.

That car doesn't have the welds in the trunk reinforced. Once those welds separate, the mounts flex and tear badly. If the plates are welded underneath but the trunk welding is still damaged, the entire floor just keeps getting hammered. We have been highly suggesting everyone that has the reinforcement done at our shop to have the trunk reinforcement done in addition to the four mounts underneath the car. We have seen a few cars that were even worse than this. One was not salvageable because the welding labor would have been cost prohibitive. one of the worst cars that we repaired had the entire diff dragging on the ground with all four mounts completely torn out of the body.

So if I understand it right, when you reinforce the subframe mount points it just moves the highest stress point outside to the trunk floor edge?
I'm just about to buy the HPF reinforcement kit but I'm nowhere near turbo M3 power levels so I hope I'll be ok.

So if I understand it right, when you reinforce the subframe mount points it just moves the highest stress point outside to the trunk floor edge?
I'm just about to buy the HPF reinforcement kit but I'm nowhere near turbo M3 power levels so I hope I'll be ok.

this is what i asked before. If this kind of failure is exclusive to boosted M cars with ridiculous power. I cant imagine a regular ass car doing that much damage.

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Quote:

Originally Posted by rohde88

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So if I understand it right, when you reinforce the subframe mount points it just moves the highest stress point outside to the trunk floor edge?
I'm just about to buy the HPF reinforcement kit but I'm nowhere near turbo M3 power levels so I hope I'll be ok.

Quote:

Originally Posted by snikwad

this is what i asked before. If this kind of failure is exclusive to boosted M cars with ridiculous power. I cant imagine a regular ass car doing that much damage.

Rear subframe failures have been a problem for a long time. Obviously, the higher hp cars will be more prone to failure, but this is a far too common occurrence even in bone stock M3's. If you just commute back and forth to work, you're probably fine. If you like to find the twisty roads on the weekend, and drive it like it was meant to be driven, you may want to be pro-active and do some type of reinforcement.

This is what I'm getting. Just got word it will arrive early next week. I'll be installing it with my new clutch and M3 rear end swap during the first week of April. Anyone in the Hampton Roads area of VA is welcome to check it out once complete.

I had the designer of this remove the "X" brace in the center, but the design is otherwise unchanged. It's made by a small company out of Cali called Mason Engineering.

imagine how those people that glued in their reinforcement kits will feel when they see this.

this is terrible

I actually considered having that done...for about 2 seconds. I ended up spending a fortune on far more welding that usual. Now I am so glad. Glue...what was I even thinking? I know they have space age epoxies out there, but this is not a situation for that.